This code system http://terminology.hl7.org/CodeSystem/risk-probability defines the following codes:

CodeDisplayDefinition
negligible Negligible likelihoodThe specified outcome is exceptionally unlikely.
low Low likelihoodThe specified outcome is possible but unlikely.
moderate Moderate likelihoodThe specified outcome has a reasonable likelihood of occurrence.
high High likelihoodThe specified outcome is more likely to occur than not.
certain CertainThe specified outcome is effectively guaranteed.
 <status value="draft"/> <experimental value="false"/> <date value="2022-02-23T19:42:18-07:00"/> <publisher value="FHIR Project team"/> <contact> <telecom> <system value="url"/> <value value="http://hl7.org/fhir"/> </telecom> </contact> <description value="Codes representing the likelihood of a particular outcome in a risk assessment."/> <caseSensitive value="true"/> <valueSet value="http://terminology.hl7.org/ValueSet/risk-probability"/> <content value="complete"/> <concept> <code value="negligible"/> <display value="Negligible likelihood"/> <definition value="The specified outcome is exceptionally unlikely."/> </concept> <concept> <code value="low"/> <display value="Low likelihood"/> <definition value="The specified outcome is possible but unlikely."/> </concept> <concept> <code value="moderate"/> <display value="Moderate likelihood"/> <definition value="The specified outcome has a reasonable likelihood of occurrence."/> </concept> <concept> <code value="high"/> <display value="High likelihood"/> <definition value="The specified outcome is more likely to occur than not."/> </concept> <concept> <code value="certain"/> <display value="Certain"/> <definition value="The specified outcome is effectively guaranteed."/> </concept> </CodeSystem>